1. Field of the Invention
The present invention generally relates to electrochemical cells, and more particularly, to a slotted insulator sheet provided in conjunction with a primary separator for preventing short circuiting of a cell under severe shock and vibration conditions, and the like.
The insulator is preferably used in conjunction with the primary separator positioned intermediate the anode and the cathode and not sealed to completely envelope either of the electrodes. The insulator of the present invention includes slots that surround the leads of one of the electrodes with a portion of the insulator sheet overlapping the primary separator to completely cover that electrode. That way, the slotted insulator in conjunction with the primary separator prevents the covered electrode from creating a short circuit condition by contacting the counter electrode or its terminal lead. For example, in a case-terminal electrode configuration with the primary separator positioned intermediate the electrodes but not completely covering either of them, should the counter electrode not terminally connected to the casing contact any one of the interior case wall, the case-terminal electrode, or the intermediate terminal lead, a short circuit will ensue. The slotted separator of the present invention is provided to prevent this from happening, particularly in a spirally wound electrode assembly.
2. Prior Art
Spirally wound electrochemical cells are manufactured from anode and cathode electrodes provided in elongate sheet or strip form having a separator material disposed therebetween and rolled up in a jellyroll-type manner. Even though the separator is wider and longer than both of the electrodes, due to manufacturing considerations, in some jellyroll constructions the separator is not sealed to envelope either of them. That can lead to short circuiting of the spirally wound electrochemical cell when one electrode telescopes or otherwise moves past the peripheral edge of the separator and comes into direct contact with the other electrode or its terminal assembly. Internal short circuiting of a cell is one of the problems that, if it occurs, results is malfunctioning of the cell and can render the associated device inoperable.
Thus, there is a need for an additional insulator structure in an electrode assembly provided at the edge of one or both of the electrodes not sealed or completely enveloped by a primary separator. Such an insulator structure is particularly useful in spirally wound and prismatic electrode configurations.